​Dynamical masses of M-dwarf binaries in young moving groups: II - Toward empirical mass-luminosity isochrones.Markus Janson, Stephen Durkan, Mickael Bonnefoy, Laetitia Rodet, Rainer Kohler, Sylvestre Lacour, Wolfgang Brandner, Thomas Henning, Julien Girardhttp://arxiv.org/abs/1811.11802Low-mass stars exhibit substantial pre-main sequence evolution during the first ~100 Myrs of their lives. Thus, young M-type stars are prime targets for isochronal dating, especially in young moving groups (YMGs), which contain large amounts of stars in this mass and age range. If the mass and luminosity of a star can both be directly determined, this allows for a particularly robust isochronal analysis. This motivates in-depth studies of low-mass binaries with spatially resolvable orbits, where dynamical masses can be derived. Here we present the results of an observing campaign dedicated to orbital monitoring of AB Dor Ba/Bb, which is a close M-dwarf pair within the quadruple AB Dor system. We have acquired eight astrometric epochs with the SPHERE/ZIMPOL and NACO instruments, which we combine with literature data to improve the robustness and precision for the orbital characterization of the pair. We find a system mass 0.66+/-0.12 Msun and bolometric luminosities in log(L/Lsun) of -2.02+/-0.02 and -2.11 +/- 0.02 for AB Dor Ba and Bb, respectively. These measurements are combined with other YMG pairs in the literature to start building a framework of empirical isochrones in mass-luminosity space. This can be used to calibrate theoretical isochrones and to provide a model-free basis for assessing relative stellar ages. We note a tentative emerging trend where the youngest moving group members are largely consistent with theoretical expectations, while stars in older associations such as the AB Dor moving group appear to be systematically underluminous relative to isochronal expectations.

So happy and proud for Jos (Jozua de Boer), my first PhD student who Yesterday defended a magnificent thesis (the blue book about "high contrast imaging of protoplanetary disks") in Leiden. We first met in 2012 and we "grew academically" together, me as ESO scientist and co-promotor (together with Prof.Dr Christoph Keller) and him as a student astronomer and now postdoc. I’m glad I could make it. PhD defenses in the Netherlands are really great. He gave a public talk in Dutch, and answered tough questions from a bunch of professors that looked as if they came out straight from the Hogwarts School of Witchcraft and Wizardry. It was a thrill to be sitting among them. Congratulations Dr de Boer and to the growing family!!!

That’s it, it’s my last -nine hundredth or so - night on Paranal, my shift number 106 (I think), in the Atacama desert in the North of Chile. At least it is the last of that chunk of lifetime.I may come back but things will be very different.I grew a lot, I am happy to leave, sad to turn this page. I will miss it so much.During these last days and nights I saw all the stuff that I like about this place.

I saw deep structures in the milky way on a moonless night, I saw the Scorpion, the Southern Cross, the Magellanic clouds, red and blue stars, meteors.I also got to see this little fox, delicate living creature of this super dry landscape.I saw green stones tinted by olivine, pink and psychedelic clouds at sunset,I saw the 4 yellow lasers coming out strongly out of UT4.I saw the flattened top of Cerro Armazones, ESO’s main focus of the next 30 to 50 years, I saw the tall and distant Llullaillaco and the now very snowy Andes towards the East.I saw computer screens, lots of them, looked at all kinds of scientific displays.

I took part of a small discovery with SPHERE and helped out with NACO, the two instruments that made me instrument scientist and grow professionally.I solved a few issues, I closed a few tickets, I called colleagues on the radio and drove a couple meetings. I got mad, I do.I showed Paranal to a friend and welcomed back Jos, my first PhD student who came back as an experienced visitor.I had interesting, sometimes intense discussions with colleagues and visitors, I ate the food, cracked some jokes, spoke Spanish, English and French equally often.I took pictures, can’t help it and I slept too little, as always.I remembered the good times, the wonderful colleagues that have left before me or who aren’t here at the moment. I also remembered the very first day I stepped the floor of the Residencia, or the control room, the first time I ran/walked up the Star Track. I slept in the plane, in the bus, spoke to the family on Skype, I rushed and procrastinated at times. I made not so unrealistic to-do lists.

Paranal is all that and more, impalpable and complex feelings of ambivalence, of beauty, intellectual sparks and social misery.Paranal is a human adventure and often a story of loneliness.Paranal is a Science spaceship in the desert with an amazing group of individuals working together, to deliver to the astronomical community.

My life as an “AstroMonk” is taking a turn only time will reveal how rich it was, how much I miss it, how much I was family-starved yet privileged to live and work in such a place, play with these fantastic , giant toys.I must let go, I must say good bye and see you next time to the ground based astronomical operations I have so much affection for.

Thank you ESO for this opportunity of a lifetime. Thank you all my colleagues, "you are the stars", literally.Thank you my family for putting up with my hectic schedule, my moods an my relative uselessness at home when I came back tired, stressed or both. Thank you to the restaurant, cleaning, maintenance and logistics personnel who put up with m…f...ers like us all the time. You made my time here so much easier and pleasant.